Sleep is like the master switch for metabolism: When you improve your sleep, every aspect of your metabolism improves; but when your sleep suffers, your entire metabolic system struggles.
Personally, lack of quality sleep impacts me more than any other poor lifestyle behaviors. Quality sleep may be more important than nutrition and exercise combined. That’s a bold statement, but I know the following to be true: I can go days without food or exercise and be just fine, but if I went days without sleep, I’d turn into a hallucinating metabolic nightmare. Sleep builds the foundation of health, and without it, the foundation will be weak. Your health will fall apart, brick by brick. Prioritizing quality sleep will supercharge every aspect of your metabolism.
My client Sandy was desperate to lose weight. He became 90 pounds overweight, developed prediabetes and high blood pressure, and relied on a sleep apnea machine each night. Sandy has a wife and teenage daughter, and he was worried about setting a bad example for them and not being around long enough to see his daughter grow up. During our first conversation, I had him share his routine with me. I discovered that he was waking up early to go to the gym before work every day. He was sacrificing sleep to exercise. I explained to Sandy that exercise is fantastic, but sleep is foundational. Exercise is something we add in once the foundations are stable. I encouraged him to stop waking up early to hit the gym and instead get those two extra hours of sleep.
Just four weeks in, Sandy was down 14 pounds by getting more sleep. He had more energy for work and family, and eventually once this sleep foundation was solid, we slowly brought in exercise. Fast-forward to today, and he’s lost 70 pounds. He no longer relies on his sleep apnea machine, and the best part, he inspired his wife, Margaret, to follow a similar lifestyle, and she went on to lose 35 pounds.
Unfortunately, many of us, like Sandy, aren’t getting enough sleep. This can disrupt our metabolic health in a number or ways, including increased insulin levels and a buildup of toxins, which we’ll explore in this chapter. I’ll also reveal the habits that wreck your sleep the most, so that you can be sure to avoid them and practice good sleep hygiene.
Sleep deprivation is an alarming issue in the United States, with about 35 percent of adults not getting the recommended seven hours of sleep each night.1 This pervasive lack of sleep has been recognized as a public health crisis by the Centers for Disease Control and Prevention (CDC). The average American now sleeps only about 6.8 hours per night, a significant decline from previous decades, reflecting a disturbing trend toward chronic sleep insufficiency.2
The repercussions of this widespread sleep deprivation are profound, affecting millions of Americans. Between 50 and 70 million adults suffer from sleep disorders, with insomnia being the most prevalent.3 Approximately 30 percent of adults experience insomnia, and 10 percent face chronic insomnia that severely impacts their daily functioning.4 This issue has far-reaching consequences for both individual health and public safety.5
Encouraging better sleep habits and prioritizing sufficient rest can lead to significant benefits, including enhanced physical health, improved mental clarity, and greater overall life satisfaction.6 As the statistics make clear, ensuring adequate sleep is a fundamental component of a healthy lifestyle, essential for maintaining optimal metabolic health and well-being.7, 8
The health implications of inadequate sleep are extensive. Sleep deprivation is linked to an increased risk of obesity, diabetes, cardiovascular diseases, and various mental health disorders. The strain on the body from lack of rest exacerbates these conditions, leading to a cycle of poor health outcomes. Moreover, sleep deprivation significantly impacts safety, contributing to nearly 20 percent of all car accidents, highlighting its role in many preventable injuries and fatalities.9
Lack of sleep contributes to metabolic dysfunction in the following four key ways:
Let’s look at each of them in turn.
Imagine your body as a well-orchestrated symphony, where each instrument represents a different aspect of your metabolism. Sleep acts as the conductor, ensuring that each instrument plays its part harmoniously. When you don’t get enough sleep, it’s as if the conductor is absent, causing the orchestra to fall out of sync. The stress hormones (like cortisol) start playing too loudly, drowning out the soft, steady rhythm of insulin, which is crucial for regulating blood sugar. Simultaneously, the hunger hormones (ghrelin and leptin) start playing erratic and conflicting tunes, leading to overeating. This chaos results in a disjointed performance in which blood sugar levels rise uncontrollably, much like a symphony gone awry without its conductor.
In one study, the authors found that after one week of shortened sleep, your blood sugar levels are disrupted so significantly that your doctor would classify you as being prediabetic. When you’re not getting quality sleep, the beta cells in your pancreas stop being sensitive to the signal of high glucose.10 Research presented at the Experimental Biology 2009 meeting highlights the link between short or poor sleep and increased risk of overeating and type 2 diabetes. Studies, such as those published in the Annals of Internal Medicine and the Journal of Clinical Endocrinology & Metabolism, and others, highlight how sleep restriction in healthy adults results in decreased insulin sensitivity and hormonal changes that increase appetite and calorie intake.11, 12, 13 These studies show that sleep deprivation disrupts appetite regulation, leading to overeating and higher insulin resistance. Stress responses and hormonal changes, including elevated stress hormones and reduced insulin, further complicate the relationship between sleep, eating behaviors, and diabetes risk.
A study published in Diabetes found that restricting sleep to five hours per night for one week significantly reduces insulin sensitivity in healthy men. The study involved 20 healthy participants and demonstrated a 20 percent reduction in insulin sensitivity following sleep restriction. This reduction was associated with increased cortisol levels but not affected by the alertness drug modafinil. The findings highlight the adverse effects of short-term sleep deprivation on glucose metabolism, raising concerns about the potential long-term impacts on insulin resistance and related metabolic disorders.14
Poor sleep elevates cortisol levels, which leads to the destruction of collagen in the skin, muscle breakdown, and bone degradation. This process supplies amino acids to the liver for glucose production, resulting in higher blood glucose levels. Consequently, this can cause insulin resistance, as the body overproduces glucose, prompting the pancreas to release insulin. Caffeine, often consumed to counteract sleep deprivation, can exacerbate cortisol production. Cortisol directly affects cells and indirectly prompts the liver to release glucose, making cells insulin resistant even without glucose changes, as observed in cell cultures treated with cortisol-like molecules.15, 16, 17
If you drink caffeinated beverages, it’s a good idea to wait at least 90 minutes after waking to consume them. Waiting 90 minutes has several benefits: It allows your body to naturally decrease cortisol levels, which are typically high upon waking. Consuming caffeine too early can further elevate cortisol, leading to increased stress and anxiety. By delaying caffeine intake, you help maintain a more balanced cortisol rhythm, enhancing alertness naturally. Additionally, this practice can prevent the midday energy crash often associated with early caffeine consumption, promoting sustained energy levels throughout the day.
Research shows that a lack of sleep can significantly slow down your metabolism, much like a car engine running inefficiently without proper maintenance. Sleep deprivation disrupts the balance of hormones related to hunger and appetite, decreasing leptin (which suppresses appetite) and increasing ghrelin (which stimulates appetite). This hormonal imbalance can lead to increased food intake and weight gain. Additionally, as we just discussed, sleep deprivation reduces insulin sensitivity, making it harder for the body to process glucose efficiently, which can result in higher blood sugar levels and an increased risk of type 2 diabetes. Inadequate sleep can lower the resting metabolic rate (RMR), which means the body burns fewer calories at rest, contributing to weight gain.
Elevated levels of cortisol (the stress hormone) due to lack of sleep, can be compared to a car’s engine overheating, causing more stress on the system. High cortisol levels can lead to increased appetite and fat storage, especially in the abdominal area. Studies have shown that individuals who sleep less tend to have higher levels of body fat. The reduction in sleep often results in fatigue and a lack of motivation to engage in physical activity, further decreasing overall energy expenditure.18 Ensuring adequate sleep is thus crucial for maintaining a healthy metabolism and preventing metabolic disorders.
Growth hormone plays a critical role in regulating metabolism, body composition, and overall health. It’s essential for stimulating growth, cell reproduction, and cell regeneration. Growth hormone promotes the synthesis of protein, which is vital for muscle growth and repair. It also increases the breakdown of fats into free fatty acids, which can be used as an energy source, thus helping to reduce body fat. Growth hormone supports the maintenance of normal blood glucose levels by reducing the uptake of glucose in tissues and enhancing glucose production in the liver. During deep sleep, also known as slow-wave sleep, growth hormone secretion is at its peak. This stage of sleep is crucial for the body’s recovery and repair processes. When individuals do not get enough deep sleep, the production of growth hormone is significantly impaired. This deficiency can interfere with various metabolic processes. For instance, inadequate growth hormone levels can lead to decreased muscle mass and increased fat accumulation. It can also impair the body’s ability to regulate blood glucose levels, increasing the risk of insulin resistance and type 2 diabetes.
Lack of deep sleep can therefore disrupt the delicate balance of metabolism. Without sufficient growth hormone, the metabolism becomes inefficient, and the body’s ability to burn fat and build muscle is compromised. This can lead to weight gain and a higher proportion of body fat. Additionally, the impaired glucose regulation associated with reduced growth hormone can exacerbate metabolic issues, further contributing to the risk of metabolic disorders. Ensuring adequate deep sleep is therefore vital for maintaining optimal growth hormone levels and supporting a healthy metabolism.
In his book Why We Sleep, Dr. Matthew Walker delves into the intricate workings of the glymphatic system, emphasizing its crucial role during sleep. The glymphatic system, a waste clearance system in the brain, becomes highly active during deep sleep. It functions similarly to the lymphatic system in the rest of the body, clearing out metabolic waste products accumulated during the day. Dr. Walker explains that during sleep, especially in the deeper stages, cerebrospinal fluid flows more freely through the brain tissue, effectively removing toxins such as beta-amyloid, which is associated with Alzheimer’s disease.
Walker highlights that the efficiency of the glymphatic system during sleep underscores the importance of adequate sleep for maintaining brain health. When we do not get enough sleep, the brain’s ability to clear out these toxins is compromised, leading to a buildup that can contribute to neurodegenerative diseases. His research points to the alarming fact that chronic sleep deprivation may increase the risk of developing Alzheimer’s disease and other cognitive impairments due to the insufficient removal of these harmful substances.
Walker’s work emphasizes that sleep quality, not just quantity, is vital for the optimal functioning of the glymphatic system. Deep, non-REM sleep is particularly important, as it is during this phase that the glymphatic system operates most efficiently. Ensuring good sleep hygiene and prioritizing deep sleep can significantly impact overall brain health, reducing the risk of cognitive decline and supporting long-term mental well-being. Walker’s research in Why We Sleep provides compelling evidence that sleep is not merely a passive state but a dynamic process essential for maintaining brain health and preventing neurodegenerative diseases.
Research strongly indicates that lack of sleep and night shift work are associated with an increased risk of various health issues, including cancer and a shortened lifespan. The World Health Organization’s International Agency for Research on Cancer (IARC) has classified night shift work as a probable carcinogen, primarily due to its disruption of the circadian rhythm.19 Circadian rhythms regulate vital physiological processes, including sleep-wake cycles, hormone release, and metabolism. Disruption of these rhythms, common among night shift workers, can lead to hormonal imbalances and impaired cellular function. Studies have shown that this disruption can increase the risk of several types of cancer, including breast, prostate, and colorectal.
The increased cancer risk among night shift workers is attributed to several mechanisms. One key factor is the suppression of melatonin, a hormone produced at night that regulates sleep and has antioxidant properties. Exposure to light at night suppresses melatonin, leading to increased oxidative stress and DNA damage, which promotes cancer development. Additionally, disrupted sleep impairs the immune system, making it less effective at detecting and destroying cancer cells. These findings highlight the critical role of maintaining regular sleep patterns and minimizing circadian disruption to mitigate cancer risk.
In addition to the increased cancer risk, lack of sleep and night shift work are associated with a shortened lifespan. Chronic sleep deprivation and circadian misalignment contribute to metabolic and cardiovascular issues, including obesity, diabetes, hypertension, and heart disease. A study published in the journal SLEEP found that individuals with irregular sleep patterns had a higher risk of mortality from all causes compared to those with regular sleep patterns.20 The cumulative effects of sleep deprivation and circadian disruption can accelerate the aging process, leading to earlier onset of age-related diseases and ultimately shortening lifespan.
Now that you understand the importance of quality sleep as it relates to metabolic health, let’s discuss some of the worst behaviors that lead to poor sleep. The first poor behavior is eating too close to bedtime. When you give your metabolism energy in the form of food and proceed not to use it because you lie down for bed, your metabolism is signaled to store every bit of that energy. Eating food raises your body temperature, which is the opposite of what you want to do before sleep. To enter deep sleep, our body temperature needs to drop by about 1 to 2 degrees Fahrenheit (approximately 0.5 to 1 degree Celsius). This drop in temperature signals to the body that it’s time to transition into the deeper stages of sleep, where restorative processes occur. The cooling down process helps facilitate the onset of sleep and maintains the optimal conditions for deep, restful sleep.
Eating before bed is like throwing a surprise party for your stomach just when it’s trying to wind down for the night. Imagine you’ve just settled into your comfy bed after a long day, ready to drift off to sleep, and suddenly, a group of friends bursts into your room, ready to party. Your peaceful night is disrupted, and instead of relaxing, you’re now wide-awake and dealing with the commotion. Similarly, when you eat right before bed, your digestive system gets a wake-up call just when it should be slowing down. The process of digestion kicks into high gear, making it harder for your body to relax and enter the deep, restorative stages of sleep. This can lead to indigestion, acid reflux, and disrupted sleep patterns, turning what should be a restful night into a restless one. Just like you wouldn’t throw a party when it’s time to sleep, it’s best to avoid eating large meals right before bed to ensure a peaceful night’s rest. I recommend no food at least three hours before bedtime.
The next bad habit is eating against your natural circadian rhythm. Circadian rhythms are the natural, internal processes that regulate the sleep-wake cycle and repeat roughly every 24 hours. These rhythms are driven by the body’s biological clocks, which are present in nearly every cell and synchronized by a master clock in the brain known as the suprachiasmatic nucleus (SCN). The SCN is located in the hypothalamus and responds primarily to light and dark signals, which help regulate various physiological processes, including hormone production, metabolism, and sleep.
Imagine your body as a quirky, bustling amusement park called “Circadian Land.” This park runs on a strict schedule set by a whimsical clock tower, the central timekeeper. This clock tower represents the brain’s suprachiasmatic nucleus (SCN), which keeps everything in sync, from the roller coasters to the snack stands. In Circadian Land, hormones are like the park’s energetic staff members. Cortisol, the park’s perky morning greeter, gets everyone pumped up and ready for a day of fun. Melatonin, the night guard, gently ushers everyone out when the park closes, ensuring things are quiet and restful for the night.
When the park follows its schedule, the rides operate smoothly, the food stands serve tasty treats on time, and everyone has a great day. But if the park’s schedule gets messed up—imagine the roller coasters running at 3 A.M. and the snack stands serving breakfast at midnight—chaos ensues. The staff gets confused, rides break down, and guests start feeling queasy. This is what happens when our circadian rhythms are disrupted by irregular sleep or eating patterns. Hormonal imbalances occur, leading to metabolic issues, weight gain, and even mood swings.21, 22
To keep Circadian Land running like a dream, it’s essential to stick to a regular schedule. Time-restricted eating is like having fixed park hours, ensuring the rides (your metabolism) and staff (hormones) work in harmony. This helps maintain balance and promotes overall health, much like a well-timed amusement park providing endless fun and joy to its visitors.23, 24
Dr. Sachin Panda, a prominent researcher in the field of circadian biology, has significantly advanced our understanding of how the body’s internal clock influences health and well-being. In his groundbreaking book, The Circadian Code, Dr. Panda explores the intricate relationship between our biological rhythms and daily habits, particularly our eating patterns.25 His research reveals that the timing of our meals can profoundly impact metabolism, weight management, and overall health. By aligning our eating schedules with our natural circadian rhythms, we can optimize bodily functions, improve energy levels, and reduce the risk of chronic diseases.
Dr. Panda’s work emphasizes that our bodies are designed to follow a 24-hour cycle, with specific times for activity, rest, and nourishment. Disrupting this cycle through irregular eating habits, such as late-night snacking or skipping meals, can lead to metabolic imbalances and health issues. Dr. Panda advocates for time-restricted eating, wherein food intake is confined to a specific window of time each day. This approach not only synchronizes our internal clocks but also enhances metabolic efficiency, supports weight loss, and lowers the likelihood of developing conditions like diabetes and heart disease. By adopting eating patterns that honor our circadian rhythms, we can harness the power of our biological clock to achieve optimal health and vitality.
Dr. Panda’s research has provided substantial insights into how the timing of food intake can affect metabolic health. One pivotal study demonstrated that mice given access to food around the clock became obese and developed various metabolic diseases, including high cholesterol, fatty liver, and diabetes. In contrast, mice that consumed the same high-fat diet but were restricted to a feeding window of 8 to 10 hours remained lean and healthy. This striking difference was attributed to better alignment with their circadian rhythms, which regulate gene expression, hormone levels, and other metabolic processes.26, 27
Incorporating Dr. Panda’s insights into our daily routines can lead to transformative changes in our health. His research underscores the importance of not just what we eat, but when we eat. By embracing a lifestyle that respects our circadian rhythms, we align ourselves with the natural order of our bodies, promoting a harmonious balance that fosters long-term well-being. As we strive for better health, understanding and implementing the principles of circadian biology can serve as a crucial foundation for achieving lasting metabolic health and overall wellness.
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Sleep is the key to unlocking your metabolic freedom. Make sure your foundation is rock solid, and everything else in this book will work that much better. Now that we’ve explored the primary causes of metabolic disease, let’s dive into the most effective solutions for restoring your metabolic health.
In Part II we’ll look at some of the solutions to these problems, starting with why keto is so valuable for metabolic health.